Learn from the Experts: Petro Design Blog

I recently saw a ‘grab’ line in an advertisement for a drainage company that stated “The most common solution to drainage is a system of French drains”.  No! This is wrong.   A French drain in the wrong location can be a costly mistake. Here are a few basic rules for handling surface drainage:

• If the area can be graded to divert the water, this should be the first approach.  A minimum of 2% slope on turf is sufficient to move water.
• If grading is not an option a surface drain, or better yet -a catch basin, could be an option.  The inlet point must still be 2% higher than the outlet point.  Excavation and distance are key financial considerations.
• For standing, percolating ground water a French drain system is a viable option.  Water takes the path of least resistance so gravel surrounding an open perforated pipe draws the water in.  The pipe still needs to be diverted to a lower elevation in order to remove the water from the area rather than just gathering it.

A turf swale is a good conductor of water

Catch basin with atrium grate to intercept surface water

French drains should not be located next to a foundation of a home for any reason.   You would think that this was common sense but I have been on 3 projects in the last 4 months where a contractor had done just that hence, drawing water into the foundation of the house.  On one project the downspouts had been tied into this foundation French drain – diverting water into the home and providing the food source for molds.

A drain tile system installed at the base of a foundation during construction is designed to divert ground water into a sump or storm water system.  This is a building code and has nothing to do with surface water.

A drysteam can be used to divert surface drainage and include a French drain system as seen below.

A ‘1000-year’ storm event is certainly the true test of the capability of a home drainage system.    Yeah, yeah “it was a freak event” yet we have had 4 ‘freak’ events in the last 6 years and it only takes 1 to add thousands of dollars in repairs or, at least, raise your insurance premiums.

Even a trickle of water in a finished basement space can ruin flooring, drywall and furnishings and feed deadly molds.

Not surprisingly, most of the damage I’ve seen, in regards to drainage, was caused by the neglect of common sense principals.

Drainage is one of the most important elements of a sound foundation and so, truly, the most cost effective preventative you can implement.

Preferably, the builder was diligent when your home was constructed.  If your home was built in the 80’s you can cross that diligence off the list.  Faulty foundation drainage may not be evident until after the home warranty has expired or until a storm ‘event’…more on this in a future blog.

It is curious to me how homeowner’s will trust their maintenance crew for resolving drainage issues.  Asking a mowing and mulching crew landscape design questions can be detrimental but relying on them for drainage correction has cost thousands in repairs.  The most cost effective job a maintenance crew should implement is gutter cleaning.  That said; I was on a project earlier this year where the client had had her maintenance company clean her gutters regularly.  Unfortunately, they cleaned only the gutters and so the bases of the downspouts were filled 4’ deep with decomposing compacted debris.  All this water had been overflowing the corrugated underground piping connections and directly into the foundation walls of the house.  Since the homeowner traveled often, she was unaware of the increasing mold growth until the basement flooded completely forcing her to remove furnishings and storage boxes from the basement thereby exposing the years of infiltration and deadly effects.  The cost was in the thousands in remediation, repairs and hotel expenses, as the odor and mold spores prevented her remaining in her home.

Piping any downspouts underground for more than 10’ should exclude the use of any interior corrugated pipe.  Corrugated piping is the black ridged piping you can easily pick up at any hardware store for about 45 cents a foot.  The ridges trap debris leading to water back-up which can freeze and settle the pipe causing even more back-ups.  There is a smooth interior walled black corrugated pipe (N12) or a number of PVC and SDR smooth walled pipes available depending on whether they will be directed under sidewalks, driveways or just soils.

Before looking down, though, it’s best to start at the top when addressing drainage issues.   Things to look ‘up’ for are:

• Undersized gutters and downspouts for the size and slope of the roof space
• Not enough downspouts for the distance of the gutter
• Gutter slope not enough to move the water
• Rivet pops from winter ice-jambs allowing water behind the gutter
• Damaged/bent gutters from winter ice jambs or falling tree limb

Confirmation of the above would be visible signs of spillage on the ground level and possible infiltration of water into the house.  Chances are if your gutters have been overflowing for some time, your foundation has settled causing even direct rain water to collect and filter into your foundation.

The next time it rains, go outside with an umbrella and look up.

To be continued…

Montgomery County Department of Environmental Protection defines pervious pavement as having more air spaces than regular pavement, allowing water to drain through the surface into the underlying soil. Most paved surfaces are currently impervious, but Environmental Site Design (ESD) efforts including installation of pervious pavement are being required for new development as well as redevelopment of properties in Montgomery County.

Applying ESD techniques such as pervious pavement in place of asphalt will help to reduce runoff and issues with flooding, as well as improve water quality. Replacing asphalt surfaces with pervious pavement can provide other ecological, social, and economic benefits.  Pervious pavement functions to slow water and allow infiltration while filtering stormwater on-site. Adding trees and vegetation in previously paved areas can provide comfortable spaces by reducing urban heat island effects and improving air quality as well as overall human health. Pervious pavements and vegetated areas help to reduce energy costs and add aesthetic appeal to any environment (www.montgomerycountymd.gov).

Petro has worked on several projects utilizing ESD techniques, including pervious pavement. Petro used pervious concrete and vegetation to help alleviate issues with pooling and flooding at a residence in Columbia, Maryland. The photo below shows the pervious concrete next to older standard concrete.